Compared are PP3 Zinc layer battery (6F23), AAAA (or similar) cells from Alkaline PP3 (6LR61), an AAA cell and an N or Lady cell (1.5V, similar size 3V lithium and 12V alkaline exist!). The N cell is too long to stack two in length and fatter than AAA, so no help at all.

Best is to open the Alkaline PP3 and cut the connector insulator in half, and cut the negative connector strip in half. Add a wire and double sided sticky foam pad to put the connector on the bottom.

It may then fit in the round case, but not if the wall is decent.

It fits easily in the squared case:

Compared to the Battery Valve boxes I have been making, this is like a battery for a dolls house!

Here it is full size! (300dpi, print so when folded it is 50mm high, each side just over 25mm, just under 1").

Fold the inner most tabs at about 47mm to 48mm spacing depending on card, as you have 3 layers of card on top and bottom!

Either print on 160mm card direct or 90gm paper and "Pritt" stick or spray mount to cereal box card.

Regard this is a prototype as I don't have a radio that uses PP4.

Pity the square version was replaced by round and that we only have the PP3, it would be nice to have 9V alkaline that was essentially 6 x AAA cells rather than the 6LR61 Alkaline as it's only 60% improvement on layer PP3 and only long life in smoke detectors.

I think the PP3 fits well diagonally in the squarer PP4 case (I tested on the one I made) and enough extra height to only just fit a PP9 sized snap top and bottom wired to PP3 connector. A 6F22 (PP3 Layer cell) is about 450mAH and a 6LR61 (PP3 Alkaline with 6 off AAAA like cells) is about 590mAH, so based on volume the Alkaline PP3 gives closer to original PP4 capacity which must have been about 700mAH to 800mAH?

A PP9 is about 5000mAH at low drain (Perhaps 3500mAH at high drain) and a PP7 maybe about 2000mAH at low drain. I use 6 x Alkaline AAA in a PP7 (about 1100mAH) and 6 x AA in a PP9 (about 2700mAH). Certainly if you soldered there is space for 12 x AA in a PP9 case.

So I will see if I can do an Octagonal PP4 case as compromise between original slightly rounded case and later cylindrical case. It can then use the round PP4 label rather than my fake square case PP4 label.

Great work there Michael, I may give this a go and if it works I will attach the original connectors to my Sky Personal as I still have these. Space is very tight in the battery compartment so may try AAA cells. I have never taken a PP4 apart as I only have one example so I think the layer cells in mine will be round as my battery is a round metal clad.

The 6 off AAA don't fit in the Octagonal-ish version, but it's only slightly more angular than the very rounded corner original version and also than the later cylindrical version. The round version label works well as it's not a regular octagon, but imagine a square with four corners cut to give the cut off bits about 1/2 of new flat sides.

The round version only takes the naked AAAA (4 As not AAA), and very tight. I think the Octagonal version is best compromise. If you squint it's round it will take PP3 in case or the 6 off AAAA out of Alkaline PP3.

Also the ends on the octagonal version are attached to the longer faces, and one end can be left unglued with tabs (You'll see the picture soon). The ends on the round version are much more awkward to attach and can't hinge

Some of the early 996 lantern batteries had those beveled corners to, A PP3 would be better and easy to work with but it may make the battery bigger so it may just fit even though its a tight squeeze. You can still buy PP4 cells but there not cheap. This size as also used in a Ferguson transistor set to as well as some test meters.

I made up connectors, and even taking the PP3 connector apart and putting a thin insulating shim under the minimal "naked" PP9 connector it's a couple of mm too long.

Using 6 off "AAAA" out of insides of Alkaline PP3 (6LR61 type) is no problem at all for height. The Kodak brand Alkaline PP3/6LR61 is too wide and distorts the Replica case slightly. All the other brands I've tried are OK.

Conclusion: The "AAAA" from a PP3 is best solution (not AAA) or if the battery compartment is large enough make the print out 3mm higher.

Well, if you trim the plastic off entirely on one side of the two PP3 connectors and bend up two opposite edges of the PP9 + terminal it's possible to get the lid folded in. Bulges a little, but sort of works and easier to refill (just plug in new PP3) than the better fitting AAAA innards solution.

Have PP3s shrunk since the 1980s?If I can remember rightly I abandoned fitting a PP3 connector because the battery would not fit in the case by a very small margin. With the can off a PP3 might well fit with an adapter.If the cells from an alkaline PP3 will re-stuff into it this could be the way to go however I will need a new snap for the negative end This is what I want it for.viewtopic.php?f=15&t=4608The leaky battery does have a good label on one side while the other side is a bit rusty.

I have never taken this size apart but I suspect it wont be easy unlike a metal clad PP9, The seal at the side is folded over and the case will loose its shape very easy, it will be like taking a metal PP3 apart which I tried on a dead Panasonic and the case just bends, that said you may just need to pick apart both ends but if the cells are stuck because of leakage it will be difficult without spoiling the case as its so fiddly. I would think the layer cells are round inside but not sure as I have never taken one apart as this battery is rare as I only have one of and its the same as yours.

There are at least 3 sizes of PP3 unfortunately,The smallest are some Layer types. About 25mm or slightly less wideMedium size are some Layer types and many Alkaline. Lidl and Aldi Alkaline PP3 do fit a B126 and virtually all Layer types do. Polariod and Sony 6F22 layer type are this size. About 25.5mm wide.Largest are some Alkaline, and a few layer type (but the internal layer biscuits same size as Medium ones I think). The Kodak Alkaline don't fit a B126 box or snap together in a chain as they are wider and thicker. Possibly up to 27.5mm wide

I think you have to open the Alkaline 6LR61 PP3 and cut off the existing PP3 connector and solder round PP9 snap to top and wire 2nd PP9 rosette snap to the bottom. Use a shim of marge tub plastic or similar for insulation.